The use of fittings for producing pipe connections is known. In this regard, the end of a pipe to be connected is fixed to the fitting. The fitting can be a pipe coupler, an angular elbow, a curved elbow, a T-connector, a wall plate or similar elements. The fitting itself can be constructed as a press fitting or a sliding sleeve or as a fitting with a sleeve made of a shape-memory alloy material. Finally, the use of threaded fittings for pipe connections is known.
All the aforementioned pipe connections have in common the fact that a pressing force is exerted inside a pressing area onto the fitting and/or the pipe to connect the pipe end to the fitting. For compression fittings, this is accomplished by radial compression of a pressing sleeve and/or a metal insert of the pipe with the aid of a pressing tool. For threaded fittings, the pressing force is realized, for example, by screwing a union nut onto a slit clamping ring that presses against the pipe from the outside. For fittings with sliding sleeves, the pressing force is created by axially pushing a non-expandable sleeve onto the widened end of the pipe that is situated on the fitting.
It is desirable for the compression state of the pipe connection to be detectable from the outside. Compression fittings with a compression marker exist in prior art, as described, for example, in WO 2004/096499 A1, DE 299 07 585 U1 and EP 1 790 896 A1. It is disadvantageous that the readout is done “by inspection.” In areas that can only be inspected visually to a limited extent, the known compression marker systems are less suitable.
From DE 198 56 769 C1, a compression pipe fitting is known that uses a contact pin as a position control element. The contact pin is arranged in such a manner that it extends radially through the wall of the compression fitting element. As soon as the conduit is at the level of the contact pin due to axial insertion, the contact pin moves radially outwards. This indicates that the conduit has been inserted sufficiently far into the compression fitting. The compression state of the compression fitting cannot be indicated by the contact pin, however.